It is common knowledge that, when dialing a phone number, the user never knows for sure which phone will ring because of different routing rules which can be applied to the dialed call, such as: immediate forwarding situation of destination, forwarding on busy situation of destination, “Do Not Disturb” situation of destination, call forwarding to private, cellular or general phone.
On a phone without a display, one only knows what the destination phone is after answer, at the callee's end, by asking the correspondent. On a phone with a display and in good situations, one may know which phone is ringing, but only when the destination phone rings. . .
Nowadays, there are essentially three different situations which can occur, as mentioned below.
Situation 1:
The user has a normal telephone without any indication about the called number. This is the most current situation.
Situation 2:
The user has a telephone with “Busy Lamp Field” functionality, allowing him to know if some other sets are idle or busy from a telephony point of view. This may give him some information on whether a call to these persons will ring their phone or not, but without being sure.
Situation 3:
Usually through a CTI (Computer Telephony Integration) application, the user may have the following information about other phones:                State of the phone: idle, ringing, busy, out of service . . .        State of the forwarding situation: no active forwarding, immediate forwarding to XXX, forward on no answer to XXX, forward on busy to XXX, “Do Not Disturb” . . .        
Although the solution provided in situation 3 is the best one known, this solution cannot be considered as being satisfactory as this solution is indeed not available to most of the subscribers, but only for those using a CTI application, that means using a computer.
Furthermore, in none of the exposed situations, not even the most sophisticated solution 3, is the caller systematically and reliably informed in advance which phone/or groups of phones, will ring when he calls a given number.